In 2009, we have advanced the objectives of this project as follows: (1) Serotype G8 virus, which can be found in cows at relatively high frequency, was first isolated in a study performed between 1979 and 1981, from stool specimens collected from children with diarrhea in Jakarta and Medan, Indonesia in association with P10 (prototype strain 69M). Since then only a few reports of such a G serotype have been published, except for many countries in Africa where it has been detected in an increasing frequency since 1997-1998. Today, G8 serotype virus has been detected on all 6 continents. Interestingly, the majority of these G8 human strains were not associated with the P10 type, but present a great diversity of P-G combinations such as G8:P8, G8:P4, G8:P6, G8:P1, G8:P2 and G8:P14. Sequence and phylogenetic analyses of the VP7 gene of various G8 virus strains have demonstrated the presence of at least four phylogenetic lineages. The study of the relationship of the phylogenetic lineages and the neutralization specificity of selected G8 strains belonging to lineage 1, 2, 3 or 4 is important because of the increasing epidemiologic importance of G8 viruses and also plans to include the G8 component in certain rotavirus vaccines (e.g., UK-based reassortant vaccine being developed in India). We generated (i) single VP7 gene substitution reassortants each of which bore 10 genes of bovine rotavirus UK strain and only the VP7 gene of one of nine G8 rotavirus strains (5 human, 3 bovine and one simian) belonging to one of four VP7 gene lineages (2 lineage 1, 1 lineage 2, 3 lineage 3 and 3 lineage 4), and (ii) hyperimmune guinea pig antiserum to each reassortant. Our results obtained by two-way cross-neutralization assays show that, unlike G9 rotavirus VP7s which display lineage-specific neutralization profiles, no significant difference in neutralization specificities is detected among the four G8 VP7 lineages tested. (2) Rotavirus genotype G1:P8 is the most commonly detected G-P combination globally. In addition, a monovalent vaccine containing genotype G1:P8 virus has been licensed recently in many countries. Increasing evidence suggests that genetic drift observed among community G1 strains is generating antigenic variants, an observation which may be important for the development of vaccination strategies. The human G1 rotavirus VP7 gene, which encodes the major protective and neutralization antigen, has been reported to belong to one of at least four phylogenetic lineages. The recently licensed monovalent vaccine contains a lineage 2 G1 virus whereas another licensed pentavalent reassortant vaccine contains a lineage 3 G1 virus. To study the relationship between the phylogenetic lineages and the neutralization specificity of selected G1 strains belonging to lineage 1, 2, 3 or 4, we generated single gene substitution reassortants each of which bore (i) 10 genes including the VP7 gene of G1 rotavirus strain and only the VP4 gene of bovine UK strain;or (ii) 10 genes of bovine UK strain and only the VP7 gene of G1 rotavirus strain belonging to one of four VP7 gene lineages (2 strains each of lineage 1, 2 or 3;and 3 lineage 4 strains). We are in the process of generating hyperimmune guinea pig antiserum to each reassortant.